Afterward, I realized that what my patient wanted was a pill that would make her lose weight. I could have prescribed her one of four drugs currently approved by the F.D.A.: two, phentermine and orlistat, that have been around for more than a decade, and two others, Belviq (lorcaserin) and Qsymia (a combination of phentermine and topiramate), that have recently come onto the market and are the first ever approved for long-term use. (Ian Parker wrote about the F.D.A.’s approval process for new medications in this week’s issue.) The drugs work by suppressing appetite, by increasing metabolism, and by other mechanisms that are not yet fully understood. These new drugs, along with beloranib—which produces more dramatic weight loss than anything currently available but is still undergoing clinical trials—were discussed with great excitement last month by experts and researchers at the international Obesity Week conference in Atlanta.

But I’ve never prescribed diet drugs, and few doctors in my primary-care practice have, either. Donna Ryan, an obesity specialist at the Pennington Biomedical Research Center at Louisiana State University, has found that only a small percentage of the doctors she has surveyed regularly prescribe any of the drugs currently approved by the F.D.A. Sales figures indicate that physicians haven’t embraced the new medications, Qsymia and Belviq, either.

The inauspicious history of diet drugs no doubt contributes to doctors’ reluctance to prescribe them. In the nineteen-forties, when doctors began prescribing amphetamines for weight loss, rates of addiction soared. Then, in the nineties, fen-phen, a popular combination of fenfluramine and phentermine, was pulled from the market when patients developed serious heart defects. Current medications are much safer, but they produce only modest weight loss, in the range of about five to ten per cent, and they do have side effects.

Still, as Ryan pointed out, doctors aren’t always shy about prescribing medications that cause side effects and yield undramatic results. A five to ten per cent weight loss might not thrill patients, or even nudge them out of being overweight or obese, but it can improve diabetes control, blood pressure, cholesterol, sleep apnea, and other complications of obesity. And, although the drugs aren’t covered by Medicare or most states’ Medicaid programs, private insurance coverage of weight-loss drugs has improved and is likely to expand further under the Affordable Care Act, which requires insurers to pay for obesity treatment. So what prevents physicians from prescribing these drugs?

Several leading experts and researchers attending Obesity Week told me that the problem is that, while specialists who study obesity view it as a chronic but treatable disease, primary-care physicians are not fully convinced that they should be treating obesity at all. Even though physicians since Hippocrates have known that excess body fat can cause diseases, the American Medical Association announced that it would recognize obesity itself as a disease only a few months ago. These divergent views on obesity represent one of the widest gulfs of understanding between generalists and specialists in all of medicine.

Lee M. Kaplan, co-director of the Weight Center at Massachusetts General Hospital, thinks that some bias comes from the average physician’s lack of appreciation for the complex physiology of weight homeostasis. Humans have evolved to avoid starvation rather than obesity, and we defend our body mass through an elaborate system involving the brain, the gut, fat cells, and a network of hormones and neurotransmitters, only a fraction of which have been identified. Obesity, Kaplan said, which represents dysfunction of this system, is likely not one disease but dozens.

That one person’s obesity is not like another’s may explain why some people lose a lot of weight with surgery, or a particular diet or drug, and some don’t. Kaplan thinks that if more doctors understood this, they’d view obesity treatment more receptively and realistically. He said, “If I were to say to you, ‘I have this drug that treats cancer,’ and you asked me, ‘What kind of cancer?,’ and I said, ‘All cancers,’ you’d laugh, because you recognize intuitively that cancer is a heterogeneous group of disorders. We’re going to look back on obesity one day and say the same thing.”

Obesity is potentially, in part, a neurological disease. Jeffrey Flier, an endocrinologist and dean of Harvard Medical School, has shown, like others, that repeatedly eating more calories than you burn can damage the hypothalamus, an area of the brain involved in eating and satiety. In other words, Big Gulps, Cinnabons, and Whoppers have altered our brains such that many people—particularly those with a genetic predisposition to obesity—find fattening foods all but impossible to resist once they’ve eaten enough of them. Louis J. Aronne, director of the Comprehensive Weight Control Program at New York-Presbyterian/Weill Cornell Medical Center, explained to me, “With so much calorie-dense food available, the hypothalamic neurons get overloaded and the brain can’t tell how much body fat is already stored. The response is to try to store more fat. So there’s very strong scientific evidence that obesity is not about people lacking willpower.”

But this message has not found its way into society, where obese people are still often considered self-indulgent and lazy, and face widespread discrimination. Several obesity experts told me they’ve encountered doctors who confide that they just didn’t like fat people and don’t enjoy taking care of them. Even doctors who treat obese patients feel stigmatized: “diet doctor” is not a flattering term. Donna Ryan, who switched from oncology to obesity medicine many years ago, recalls her colleagues’ surprise. “I had respect,” she says. “I was treating leukemia!”

George Bray, also of the Pennington Biomedical Research Center, thinks that socioeconomic factors play into physicians’ lack of enthusiasm for treating obesity. Bray points to the work of Adam Drewnowski at the University of Washington, who has shown that obesity is, disproportionately, a disease of poverty. Because of this association, many erroneously see obesity as more of a social condition than a medical one, a condition that simply requires people to try harder. Bray said, “If you believe that obesity would be cured if people just pushed themselves away from the table, then why do you want to prescribe drugs for this non-disease, this ‘moral issue’? I think that belief permeates a lot of the medical field.”

Obesity experts with whom I spoke tended to be more optimistic than other physicians about the possibility that obesity can be treated successfully and that the obesity epidemic will be curbed. They point to exciting new research—for example, the finding that an alteration in gut bacteria, rather than mechanical shrinking of the stomach or intestine, may be what causes weight loss after gastric bypass. This raises the possibility that the benefits of surgery might become available without the surgery itself. They also note that public-health efforts seem to be reducing childhood obesity, even in poor communities. But they remain concerned that despite such promising developments, many physicians still don’t see obesity the way they do: as a serious, often preventable disease that requires intensive and lifelong treatment with a combination of diet, exercise, behavioral modification, surgery, and, potentially, drugs.

Louis Aronne thinks this will change as more physicians enter the field of obesity medicine, the physiology of obesity is better understood, and more effective treatment options become available. He likens the current attitude toward obesity to the prevailing attitude toward mental illness years ago. Aronne remembers, during his medical training, seeing psychotic patients warehoused and sedated, treated as less than human. He predicts that, one day, “some doctors are going to look back at severely obese patients and say, ‘What the hell was I thinking when I didn’t do anything to help them? How wrong could I have been?’ ”

Patients like the woman who asked me to help her lose weight may not have to wait that long. Specialists are now developing programs to aid primary-care physicians in treating obesity more aggressively and effectively. But we’ll have to want to treat it: as Kaplan argues, “Whether you call it a disease or not is not so germane. The root problem is that whatever you call it, nobody’s taking it seriously enough.”

Suzanne Koven is a primary-care doctor at Massachusetts General Hospital in Boston and writes the column “In Practice” at the Boston Globe.